This study aimed to explore engineering students' self-directed learning abilities in an online learning environment. The research centered on the correlation relationship between students' self-directed learning abilities and learning outcomes. The instructional activity in one experimental study was to simulate an online learning task in the real-world online courses. The results of the study showed that a significant, positive relationship existed between engineering students' self-directed learning abilities and online learning performances. High level of self-directed students performed better in the criterion test.